For optimum performance of two-cycle internal combustion engines under different load or operating conditions, it is desirable to vary the timing for opening and/or closing the exhaust, transfer or fuel intake ports depending upon the operating conditions. For instance, it is desirable to open the exhaust port later during the expansion stroke of the piston for maximum power and fuel efficiency at lower engine speeds and to open the exhaust port earlier during the expansion stroke when the engine is operating under lower load, higher speed conditions. Variations of the timing of transfer port opening is desirable under certain operating conditions for optimization of power and fuel economy. For two-cycle engines having a fuel intake port controlled by the piston, early opening of the intake port is more desirable for high speed power, whereas later opening of the intake port is more desirable for lower speeds.
Examples of prior art constructions for varying the timing of the opening and/or closing of various ports in the cylinder a two-cycle internal combustion engine are disclosed in the Still U.S. Pat. No. 1,514,476 issued Nov. 4, 1924 and the Meulien U.S. Pat. No. 2,714,879 issued Aug. 9, 1955.
Examples of prior art constructions for two-cycle internal combustion engines including a valve in an exhaust, a fuel intake passage or, a transfer passage for controlling flow from or into the engine cylinder are disclosed in the following U.S. patents:
______________________________________ PATENTEE PAT. NO. ISSUE DATE ______________________________________ Woolerg 1,101,374 June 23, 1914 McCabe 1,743,558 January 14, 1930 Ewing 1,912,574 June 6, 1933 Garve 2,189,106 February 6, 1940 Onishi 3,817,227 June 18, 1974 ______________________________________